Method of making hobs



J. EDGAR 2,185,839

METHOD 0F MAKING HOBS original Filed June so, 195o 2 sheets-sheet 1 ATTORNEYS Jan.2,1940. J EDGAR 2,185,839

METHOD 0F MAKlNG HoBs iginal Filed June 30, 1930 '2 Slieets-Sheet 2 I l ENTOR l J0 d ar' BY y ATToRNEYs Patented Jan. 2, 1940 PAT-ENT OFFICE METHOD MAKING HOBS John Edgar, Rockford, Ill.,lassignor to Barber- Colman Company, Rockford, Ill., ar corpora-` tion of Illinois Original application June' 30, 1930, Serial No. 464,856, now Patent No. 2,010,353, dated August 6, 1935. Divided and this 1935, Serial No. 29,590

application July 3,

v claims. (ci. 'r6- 101) p in Fig. 6, with 'the ratchet produced thereby This invention relates in general to methods ci making metal cutting `tools and more particularly to a method of making hobs for cutting ratchets orthe like.

- l The present application is a division of my original application, Serial No. 464,856, filed June 30, 1930, now Patent No. 2,010,353, issued August 6, 1935.

`In ratchets, or the like, the root portions between the teeth sometimes are other in form than cylindrical and concentric about the axis of the ratchet. lindrical but eccentric to the axis of the ratchet. In this instance, each root portion has a difierent center, but the respective-centers are similarly spaced about the axis of the ratchet. The root. portions also may bev non-cylindrical in form, as for example in the form of plane surfaces.

Heretofore, it has lbeen limpossibile to hob ratchets of the general formin` whichl the root portions were other than cylindrical and conn centric with the axis of rotation without developing large llets at the junctions of the root portions and the sides of the teeth, This fault was particularly pronounced where the tooth depth was great as compared with the width of the-tooth space.

It is, therefore, the general object of the invention to provide a method of making an improvedwhob of the type required to generate ratchets, and the like, of the above described form. y

Another object is to provide a method of making a hob of this character which will generate a ratchet having no objectionable llets between ing the features of the invention, and-shown in progressive operative relation to a ratchet.

Fig. 4 is an end elevation of the hob with the ratched generated thereby shown in dotted lines in operative relation thereto.

Figs. 5, 5a and 5b are fragmentary radial'sec-v tions illustrating the positions forming the hob.

Fig. 6 is a view similar to Fig. 4 showing a modied form of hob with the ratchet generated thereby shown in dotted lines in operative relation thereto.v

of the tool in Fig. 7 is an end elevation of the hob shown Thus, these root portions may be cy- Ashown in dotted lines. I

Figs. 8, 8a, and 8b illustrate various positions'.

or" the tool in forming the modied form of hob.

4I-Ieretofore-,hobs for generating ratchetswere unable to4 generate the root portion with sharp corners between the sides ofthe teeth and the root portion. The outer ends of thehob teeth for vthe root portion ofthe ratchet,jwhile the sides ofthe hob teeth form the sides of the ratchet-teeth. Hence, in order to give the desiredv shape to the root -portion of the ratchet, it is necessary to modify the outer ends of the hob teeth. In theimprovedhob, herein dis.- closed, the outer ends of the hob teeth are so modified that they will form the desired root porticnof the ratchet. This is accomplished by separate and additional `operations in forming the hob. l

The ratchet, shown at I in Figs. l to 4 of the drawings, illustrates a type that may be formed by a hob made by the method herein disclosed.

This ratchet-has teeth II with straight sides, one of which generally lies on a radius as shown at I2 in order to provide a proper abutment for a cooperating pawl (not shown). pair of adjacent teeth III, the bottom or root portion I3 is circular in form with its center M oiiseta predetermined distance from the axis I of the ratchet.v Each root portion I3 has a different, center I4, but all the centers I4 are similarly disposed relative tothe axis I5 of the ratchet so that they lie in a circle concentric to the axis I5.

To generate this ratchet, a hob is Iproduced which is standard in all respects except that the tooth depth is greaterkthan necessary to produce a root portion of a predetermined shape, in order 4 to yproduce keys' having straight sides extend- Between each transverse gashes in the blank, and relieving lthe teeth. The interfering portions of the teeth superimposing a ends of the elongated teethof the hob. In the case of making a hobI to form the ratchet I0, the

form tool hasa circular contour having afcenter 22 and a radius substantially equal to the radius ofthe roo-t portions I3 of the ratchet to be generated. For the turning operation, the form tool 2D is mounted with its eiective cutting edge in an axial plane of the hob for swinging movement in said plane on an axis 2l bearing the same relation to the center 22 that the axis I5 of the ratchet bears to the center I4 of the root portion. The hob is rotated about its own axis and simultaneously the tool is swung about the axis 2| through an angle equal to the circular pitch of the teeth of the ratchet for each revolution of the hob.

At the start of the turning operation, the form tool is spaced from the hob-axis suliciently to permit removal of a suitable amount of metal. However,A after the swinging movement, the tool and hob are shifted relatively nearer to each` other and the swinging movement of the tool and rotation of the hob is repeated to remove more metal. This cycle of simultaneously swinging the tool and rotating the hob, and then the relative shifting movement is repeated until the axis 2| is moved to a point relative to the hob corresponding to the position of the axis l5 of the ratchet relative to the hob during the hobbing operation.

Theoretically, the tool should lie in a plane perpendicular to the helix of the hob in order to form a groove or depression therein of a circular contour in said plane, and the swinging of the tool should be in said plane. Thus, a groove would be cut having an elliptical contour in an axial plane. But a close approximation of such form can be obtained by swinging the tool in an axial plane as described, and making the radius of the circular contour of the tool slightly greater than that theoreticaliy required.

'Ihis turning operation cuts a peripheral helical groove in the hob of a constant lead in the same direction as, but less in' degree than, the lead of the thread of the teeth. The centers of successive transverse contours of the teeth are located progressively along a helix about .a circular line which is concentric with the hob axis and which is located in a transverse planeof the hob.

In Figs. 6 and '7 a modied form of hob is shownwhich'is adapted to generate a ratchet 25 in which the root portion 26 is straight. For this hob, a form tool 21, which is used to turn away the interfering portions of the teeth, (Figs, 8, 8a and 8b) has a form corresponding to the root portion 25 ofthe ratchet 25, which form is a straight line, and the tool is swung during the turning operation about an axis 28 corresponding to the axis of the ratchet 25 in the same manner as was previously described.

It is apparent from the foregoing that I have provided a new and improved method of making a hob which will generate a ratchet or the like having a root portion other in form than cylindrical and concentric with the axis of the ratchet. It is also evident that such a ratchet has no objectionable iillets between vthe sides of the teeth and the root portions of they ratchet,

I claim as my invention:

l. The method of making a hob for generating ratchets or the likecomprising threading and gashing a blankand relieving the teeth thereon, rotating said blank about its axis and feeding a form tool by a swinging movement in a predetermined plane including the axis of the hob into engagement with said teeth to cut a groove therein, said groove having a circular contour in any plane including the axis of the hob, the circular contour in said predetermined plane being eccentric to the axis of swinging.

2. The method of making a hob for generating ratchets or the like, which includes threading, gashing and relieving a blank to form teeth thereon, rotating said blank about its axis and removing a portion of said teeth by a tool having ka form substantially the same as the root portion of theratchet and swinging said tool about an axis corresponding to the axis of the ratchet, the axis of rotation of the tool being eccentric to the form of the tool in the same manner that the axis of the ratchet is spaced from the center of the circular form of the root portion of the ratchet.

3. The method of making a hob for generating ratchets or the like, which includes. threading, gashing and relieving a blank to form teeth thereon, rotating said blank about its axis and removing a portion of said teeth by a tool having a circular form whose center corresponds to the center of a root portion of the ratchet, said tool being swung in av plane including-the axis of the hob and around an axis corresponding to-the axis of the ratchet through an angle for each revolution of the hob equal to the circular pitch of the ratchet.

4. The method of making a hob for generating teeth comprising rotating the hob about its axis and turning the hob by means of a form tool of a circular contour which is swung in an axial plane, the center for said contour being eccentric to the axis of swinging. l

5. The method of making a hob for generating tooth sections of a ratchet or the likewhich comprises forming teeth on the hob, providing a form tool having an arcuate cutting edge, mounting said tool for swinging movement about an axis eccentric to the center of curvature of said arcuate cutting edge and perpendicular to an axial plane of the hob with said cutting edge lying in said plane, and simultaneously imparting to the tool said swinging movement and rotating the hob about its axis in timed relation to remove portions of the teeth of the hob.

6. The method of making a hob for generating tooth sections of a ratchet or the like comprising forming teeth on the hob, providing a form tool having a cutting edge of substantially the same shape as the root portion of the ratchet,.mount ing said tool to swing on an axis bearing the same relation to said cutting edge as the axis of the ratchet bears to the root portion thereof and perpendicular to an axial plane of the hob, rotating said hob about its axis, moving 'said tool about said axis of swinging through angles equal to the circular pitch of the ratchet teeth for each revolution of the hob, and bodily sluiting said tool toward the hob between each angular movement of the tool until said axis of swinging bears the same relation to the `hob axis as the ratchet axis bears to the hob axis during the hobbing operation.

7. The method of making a hob ior generating teeth comprising rotating the hob about its axis, and feeding a straight-edged form tool into cutting engagement with the teeth of the hob by a swinging movement about an axis located at one side of a normal to the line of contact of the tool and the hob teeth at the center of said line.

JOHN EDGAR. 

